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Network Security is an important part of network management and is gaining more significance as businesses come to rely more on Information Technology. In order to gain comprehensive network security it is important to gain an understanding of the threat to the networks. The OSI reference model describes seven layers of network protocol design.

Each layer is responsible for providing a series of functions to other layers, in assembling a packet for transmission. However, if the functionality of any of this layer is blocked or restricted, then the functionality of all the layers become restricted, denying a device service to the network. Various types of attacks are used to carry out malicious activities through which a network access of a device is blocked. These attacks make use of vulnerabilities in different layers of the implemented protocol. This paper takes describes the vulnerabilities of the physical layer and MAC part of the data link layer of the OSI model, how these vulnerabilities can be overcome and how the solution work.

Physical Layer and Vulnerabilities

The Physical layer is the lowest layer of the OSI model. The physical layer defines the mechanical aspects of network connection which include type of connectors, latches as well as circuit-to-circuit assignment. The physical layer is also responsible for defining electrical aspects such as voltage levels which define the binary values, grounding aspect as well as transmission of bits across the medium being utilized (Boyles).

At physical layer, Denial-of-Service attacks can be carried out by attackers in order to deny a device of resource which it can use to transmit data. This kind of attack is not very common on wired networks, as it requires directly access the medium of transmission, but wireless medium is much more vulnerable. One of the most commonly used wireless standards is the 802.11 Wireless LAN. This standard specifies a limited number of frequencies to be used for transmission. Hence, these frequencies can easily be saturated with noise produced through inexpensive devices, reducing the signal-to-noise ratio to undesirable level and denying the use of any frequencies by devices on the network. The only way to get rid of the jamming is to get rid of the noise producing device (Tipton and Krause).

Another security issue that exists in the physical layer is of eavesdropping. Eavesdropping refers to the interception and viewing of the data transmitted on to the medium. This type of vulnerability is also commonly found in the wireless networks. If a listening device can be tuned to the frequency on which a transmission is taking place that all the messages which are exchanged between difference entities on a wireless network can be heard. Fake messages can also be injected into the network (Joshi ). The problem of eavesdropping can be mitigated by using encryption on the data packets which are sent over the network. Encryption converts the data into a form that is unreadable to an eavesdropper even if it gets to read the data. It usually requires the use of a special set of number called keys to convert the data into a form that is readable by the receiver (decryption).  A number of technologies are available which can be used to secure network services. For example, SSL can be used to secure web traffic and  SSH can be used to provide secure  remote connectivity. The security of the encrypted depends upon the length of the key used for encryption of data (Tipton and Krause).

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